Recently, cells having a light weight, a long service life and a high energy density are particularly demanded as a main power source or an auxiliary power source for electric automobiles and fuel cell vehicles, or as a power source for small-size electronics devices. For this demand, a non-aqueous electrolyte cell using lithium as an active substance for a negative electrode is known as one of the cells having a high energy density because an electrode potential of lithium is lowest among metals and an electric capacity per unit volume is large, and many kinds of such a cell are actively studied irrespectively of primary cell and secondary cell, and a part thereof is practiced and supplied to markets. For example, the non-aqueous electrolyte primary cells are used as a power source for cameras, electronic watches and various memory backups. Also, the non-aqueous electrolyte secondary cells are used as a driving power source for note-type personal computers, mobile phones and the like, and further they are investigated to use as the main power source or the auxiliary power source for the electric automobiles and the fuel cell vehicles.
In these non-aqueous electrolyte cells, since lithium as an active substance for a negative electrode violently reacts with a compound having an active proton such as water, alcohol or the like, an electrolyte used in these cells is limited to an aprotic organic solvent such as ester compound, ether compound or the like. Although the aprotic organic solvent is low in the reactivity with lithium as the active substance for the negative electrode, there is a high risk that if a large current flows violently, for example, in the short-circuiting or the like and the cell generates abnormal heat, the aprotic organic solvent is vaporized and decomposed to generate a gas, or the generated gas and heat cause explosion and ignition of the cell, fire is caught by a spark generated in the short-circuiting or the like.
On the contrary, there is developed a non-aqueous electrolyte cell in which a phosphazene compound is added to a non-aqueous electrolyte for the cell so as to give non-combustibility, flame retardance or self-extinguishing property to the electrolyte, whereby the risk of igniting-firing the cell in an emergency such as the short-circuiting or the like is highly reduced (see JP-A-H06-13108).
Moreover, a separator is used in the above-mentioned non-aqueous electrolyte secondary cell for preventing the contact between a positive electrode and a negative electrode. As the separator is used a porous thin-layer film or the like not obstructing ionic migration in the electrolyte. However, the thin-layer film does not have an ability of holding the electrolyte, so that there is a risk of liquid leakage in the cells using the thin-layer film as a separator.
On the contrary, polymer cells using a polymer for an electrolyte are recently developed as a cell having no fear of liquid leakage. Particularly, the polymer cell is recently and increasingly studied because the formation of film is possible and the assembling property into an electronic device is good and the effective utilization of spaces is possible in addition to no fear of liquid leakage. As the electrolyte used in the polymer cell, there are known a true polymer electrolyte formed by carrying a lithium salt on a polymer, and a gel electrolyte formed by swelling a polymer with an organic solvent. However, the true polymer electrolyte has a problem that an ion conductivity is considerably lower than that of the gel electrolyte. On the other hand, in the polymer cell using the gel electrolyte, since a lithium metal or a lithium alloy is used as a material for a negative electrode likewise the aforementioned non-aqueous electrolyte secondary cell and such a negative electrode violently reacts with a compound having an active proton such as water, alcohol or the like, the organic solvent used in the gel electrolyte is limited to an aprotic organic solvent such as ester compound, ether compound or the like. Although the aprotic organic solvent is low in the reactivity with lithium as the active substance for the negative electrode, there is a high risk that if a large current flows violently, for example, in the short-circuiting or the like and the polymer cell generates abnormal heat, the aprotic organic solvent is vaporized and decomposed to generate a gas, or the generated gas and heat cause explosion and ignition of the cell, fire is caught by a spark generated in the short-circuiting or the like.
On the contrary, there is developed a polymer cell in which a phosphazene compound is added to an electrolyte for the polymer cell so as to give non-combustibility, flame retardance or self-extinguishing property to the electrolyte, whereby the risk of igniting-firing the polymer cell in an emergency such as the short-circuiting or the like is highly reduced (see WO 03/005478A).